wireproto: support /api/* URL space for exposing APIs

I will soon be introducing a new version of the HTTP wire protocol.
One of the things I want to change with it is the URL routing.
I want to rely on URL paths to define endpoints rather than the
"cmd" query string argument. That should be pretty straightforward.

I was thinking about what URL space to reserve for the new protocol.
We /could/ put everything at a top-level path. e.g.
/wireproto/* or /http-v2-wireproto/*. However, these constrain us
a bit because they assume there will only be 1 API: version 2 of
the HTTP wire protocol. I think there is room to grow multiple
APIs. For example, there may someday be a proper JSON API to query
or even manipulate the repository. And I don't think we should have
to create a new top-level URL space for each API nor should we
attempt to shoehorn each future API into the same shared URL space:
that would just be too chaotic.

This commits reserves the /api/* URL space for all our future API
needs. Essentially, all requests to /api/* get routed to a new WSGI
handler. By default, it 404's the entire URL space unless the
"api server" feature is enabled. When enabled, requests to "/api"
list available APIs. URLs of the form /api/<name>/* are reserved for
a particular named API. Behavior within each API is left up to that
API. So, we can grow new APIs easily without worrying about URL
space conflicts.

APIs can be registered by adding entries to a global dict. This allows
extensions to provide their own APIs should they choose to do so.
This is probably a premature feature. But IMO the code is easier
to read if we're not dealing with API-specific behavior like config
option querying inline.

To prove it works, we implement a very basic API for version 2
of the HTTP wire protocol. It does nothing of value except
facilitate testing of the /api/* URL space.

We currently emit plain text responses for all /api/* endpoints.
There's definitely room to look at Accept and other request headers
to vary the response format. But we have to start somewhere.

Differential Revision: https://phab.mercurial-scm.org/D2834

tests/test-http-api-httpv2.t

@@ -0,0 +1,65 b''
+  $ send() {
+  >   hg --verbose debugwireproto --peer raw http://$LOCALIP:$HGPORT/
+  > }
+
+  $ hg init server
+  $ cat > server/.hg/hgrc << EOF
+  > [experimental]
+  > web.apiserver = true
+  > EOF
+  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+
+HTTP v2 protocol not enabled by default
+
+  $ send << EOF
+  > httprequest GET api/exp-http-v2-0001
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/exp-http-v2-0001 HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 404 Not Found\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 33\r\n
+  s>     \r\n
+  s>     API exp-http-v2-0001 not enabled\n
+
+Restart server with support for HTTP v2 API
+
+  $ killdaemons.py
+  $ cat > server/.hg/hgrc << EOF
+  > [experimental]
+  > web.apiserver = true
+  > web.api.http-v2 = true
+  > EOF
+
+  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+
+Requests simply echo their path (for now)
+
+  $ send << EOF
+  > httprequest GET api/exp-http-v2-0001/path1/path2
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/exp-http-v2-0001/path1/path2 HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 12\r\n
+  s>     \r\n
+  s>     path1/path2\n

tests/test-http-api.t

@@ -0,0 +1,201 b''
+  $ send() {
+  >   hg --verbose debugwireproto --peer raw http://$LOCALIP:$HGPORT/
+  > }
+
+  $ hg init server
+  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+
+Request to /api fails unless web.apiserver is enabled
+
+  $ send << EOF
+  > httprequest GET api
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 404 Not Found\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 44\r\n
+  s>     \r\n
+  s>     Experimental API server endpoint not enabled
+
+  $ send << EOF
+  > httprequest GET api/
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/ HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 404 Not Found\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 44\r\n
+  s>     \r\n
+  s>     Experimental API server endpoint not enabled
+
+Restart server with support for API server
+
+  $ killdaemons.py
+  $ cat > server/.hg/hgrc << EOF
+  > [experimental]
+  > web.apiserver = true
+  > EOF
+
+  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+
+/api lists available APIs (empty since none are available by default)
+
+  $ send << EOF
+  > httprequest GET api
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 100\r\n
+  s>     \r\n
+  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
+  s>     \n
+  s>     (no available APIs)\n
+
+  $ send << EOF
+  > httprequest GET api/
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/ HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 100\r\n
+  s>     \r\n
+  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
+  s>     \n
+  s>     (no available APIs)\n
+
+Accessing an unknown API yields a 404
+
+  $ send << EOF
+  > httprequest GET api/unknown
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/unknown HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 404 Not Found\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 33\r\n
+  s>     \r\n
+  s>     Unknown API: unknown\n
+  s>     Known APIs: 
+
+Accessing a known but not enabled API yields a different error
+
+  $ send << EOF
+  > httprequest GET api/exp-http-v2-0001
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/exp-http-v2-0001 HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 404 Not Found\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 33\r\n
+  s>     \r\n
+  s>     API exp-http-v2-0001 not enabled\n
+
+Restart server with support for HTTP v2 API
+
+  $ killdaemons.py
+  $ cat > server/.hg/hgrc << EOF
+  > [experimental]
+  > web.apiserver = true
+  > web.api.http-v2 = true
+  > EOF
+
+  $ hg -R server serve -p $HGPORT -d --pid-file hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+
+/api lists the HTTP v2 protocol as available
+
+  $ send << EOF
+  > httprequest GET api
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 96\r\n
+  s>     \r\n
+  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
+  s>     \n
+  s>     exp-http-v2-0001
+
+  $ send << EOF
+  > httprequest GET api/
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/ HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 96\r\n
+  s>     \r\n
+  s>     APIs can be accessed at /api/<name>, where <name> can be one of the following:\n
+  s>     \n
+  s>     exp-http-v2-0001

mercurial/configitems.py

@@ -580,6 +580,12 b" coreconfigitem('experimental', 'update.a"
 coreconfigitem('experimental', 'sshpeer.advertise-v2',
     default=False,
 )
+coreconfigitem('experimental', 'web.apiserver',
+    default=False,
+)
+coreconfigitem('experimental', 'web.api.http-v2',
+    default=False,
+)
 coreconfigitem('experimental', 'xdiff',
     default=False,
 )

mercurial/hgweb/hgweb_mod.py

@@ -320,6 +320,13 b' class hgweb(object):'
             # replace it.
             res.headers['Content-Security-Policy'] = rctx.csp
 
+        # /api/* is reserved for various API implementations. Dispatch
+        # accordingly.
+        if req.dispatchparts and req.dispatchparts[0] == b'api':
+            wireprotoserver.handlewsgiapirequest(rctx, req, res,
+                                                 self.check_perm)
+            return res.sendresponse()
+
         handled = wireprotoserver.handlewsgirequest(
             rctx, req, res, self.check_perm)
         if handled:

mercurial/wireprotoserver.py

@@ -33,6 +33,7 b" HGTYPE = 'application/mercurial-0.1'"
 HGTYPE2 = 'application/mercurial-0.2'
 HGERRTYPE = 'application/hg-error'
 
+HTTPV2 = wireprototypes.HTTPV2
 SSHV1 = wireprototypes.SSHV1
 SSHV2 = wireprototypes.SSHV2
 
@@ -214,6 +215,75 b' def handlewsgirequest(rctx, req, res, ch'
 
     return True
 
+def handlewsgiapirequest(rctx, req, res, checkperm):
+    """Handle requests to /api/*."""
+    assert req.dispatchparts[0] == b'api'
+
+    repo = rctx.repo
+
+    # This whole URL space is experimental for now. But we want to
+    # reserve the URL space. So, 404 all URLs if the feature isn't enabled.
+    if not repo.ui.configbool('experimental', 'web.apiserver'):
+        res.status = b'404 Not Found'
+        res.headers[b'Content-Type'] = b'text/plain'
+        res.setbodybytes(_('Experimental API server endpoint not enabled'))
+        return
+
+    # The URL space is /api/<protocol>/*. The structure of URLs under varies
+    # by <protocol>.
+
+    # Registered APIs are made available via config options of the name of
+    # the protocol.
+    availableapis = set()
+    for k, v in API_HANDLERS.items():
+        section, option = v['config']
+        if repo.ui.configbool(section, option):
+            availableapis.add(k)
+
+    # Requests to /api/ list available APIs.
+    if req.dispatchparts == [b'api']:
+        res.status = b'200 OK'
+        res.headers[b'Content-Type'] = b'text/plain'
+        lines = [_('APIs can be accessed at /api/<name>, where <name> can be '
+                   'one of the following:\n')]
+        if availableapis:
+            lines.extend(sorted(availableapis))
+        else:
+            lines.append(_('(no available APIs)\n'))
+        res.setbodybytes(b'\n'.join(lines))
+        return
+
+    proto = req.dispatchparts[1]
+
+    if proto not in API_HANDLERS:
+        res.status = b'404 Not Found'
+        res.headers[b'Content-Type'] = b'text/plain'
+        res.setbodybytes(_('Unknown API: %s\nKnown APIs: %s') % (
+            proto, b', '.join(sorted(availableapis))))
+        return
+
+    if proto not in availableapis:
+        res.status = b'404 Not Found'
+        res.headers[b'Content-Type'] = b'text/plain'
+        res.setbodybytes(_('API %s not enabled\n') % proto)
+        return
+
+    API_HANDLERS[proto]['handler'](rctx, req, res, checkperm,
+                                   req.dispatchparts[2:])
+
+def _handlehttpv2request(rctx, req, res, checkperm, urlparts):
+    res.status = b'200 OK'
+    res.headers[b'Content-Type'] = b'text/plain'
+    res.setbodybytes(b'/'.join(urlparts) + b'\n')
+
+# Maps API name to metadata so custom API can be registered.
+API_HANDLERS = {
+    HTTPV2: {
+        'config': ('experimental', 'web.api.http-v2'),
+        'handler': _handlehttpv2request,
+    },
+}
+
 def _httpresponsetype(ui, req, prefer_uncompressed):
     """Determine the appropriate response type and compression settings.
 

mercurial/wireprototypes.py

@@ -9,9 +9,10 b' import abc'
 
 # Names of the SSH protocol implementations.
 SSHV1 = 'ssh-v1'
-# This is advertised over the wire. Incremental the counter at the end
+# These are advertised over the wire. Increment the counters at the end
 # to reflect BC breakages.
 SSHV2 = 'exp-ssh-v2-0001'
+HTTPV2 = 'exp-http-v2-0001'
 
 # All available wire protocol transports.
 TRANSPORTS = {
@@ -26,6 +27,10 b' TRANSPORTS = {'
     'http-v1': {
         'transport': 'http',
         'version': 1,
+    },
+    HTTPV2: {
+        'transport': 'http',
+        'version': 2,
     }
 }